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The following is a grammar for regular expressions over symbols $a$ and $b$ only, using $+$ in place of $\mid$ for union, to avoid conflict with the use of vertical bar as a metasymbol in grammars:

  • $rexpr\rightarrow rexpr+rterm\mid rterm$ 
  • $rterm\rightarrow rterm\:rfactor\mid rfactor$
  • $rfactor\rightarrow rfactor \:\ast\mid rprimary$
  • $rprimary\rightarrow a\mid b$
  1. Left factor this grammar.
  2. Does left factoring make the grammar suitable for top-down parsing?
  3. In addition to left factoring, eliminate left recursion from the original grammar.
  4. Is the resulting grammar suitable for top-down parsing? 
in Compiler Design by Veteran (59.1k points) | 35 views

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